青藏高原东北部贵德盆地上新世沉积环境分析及其意义

青海贵德盆地发育巨厚的新生代地层,在青藏高原北部具有很好的代表性,其中含较丰富的重要哺乳动物化石,对确定盆地及周边相似地层的年代、高原隆升过程具有重要的科学意义.结合哺乳动物采用典型剖面精确古地磁测年为基础的时间框架,通过盆地沉积层序、沉积相和沉积演化以及其对构造和气候变化响应的研究表明:6.5～约1.8MaB.P.期间盆地沉积环境变化经历了8个阶段的演化,反映在此期间青藏高原北部经历了＞5.4MaB.P.、3.6MaB.P.、2.6MaB.P.和1.8MaB.P.4次明显的构造挤压隆升运动,其中约1.8MaB.P.的构造运动可能使黄河向上游溯源侵蚀,同时切穿积石峡、李家峡和松巴峡而到达贵德盆地.研究时段内气候以干旱为主,但在6.2～4MaB.P.和2.1～1.85MaB.P.的两个时期气候明显湿润.

PLIOCENE SEDIMENTARY ENVIRONMENT OF THE GUIDE BASIN ON THE NORTHEAST MARGIN OF THE QINGHAI-TIBETAN PLATEAU AND ITS SIGNIFICANCE

The huge thick Cenozoic strata in the Guide basin, located in the northern of the Tibetan Plateau, contain important mandible fossils that are favorable for studying ages of relevant strata and the uplift process of the plateau. Nineteen lithofacies, four sedimentary environments and eight stages of sedimentary environment evolution are recognized in this sequence of Cenozoic strata. Four tectonic uplift events accompanied with climatic changes occurred from 6.5 to 1.8 Ma B.P.: >5.4 Ma B.P., 3.6 Ma B.P., 2.6 Ma B.P., and 1.8 Ma B.P. The tectonic uplift at about 1 8Ma B.P. might lead to the upper Yellow River's headward erosion to cut through the Jishixia gorge, the Lijiaxia gorge and the Songbaxia gorge, and the Yellow River appeared in the Guide basin. The climate was mainly dry in 6.5～1.8 Ma B.P., but became wet in about 5.4～4 Ma B.P. and 2.1～ 1.85 Ma B.P.